/*
 * Created on Nov 1, 2011
 * Created by Paul Gardner
 * 
 * Copyright (C) Azureus Software, Inc, All Rights Reserved.
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License only.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */

package com.aelitis.azureus.core.util;

import java.util.HashMap;
import java.util.Map;
import java.util.Stack;
import java.util.regex.Pattern;

import org.gudy.azureus2.core3.util.Debug;

public class RegExUtil {
    private static ThreadLocal<Map<String, Object[]>> tls = new ThreadLocal<Map<String, Object[]>>() {
        public Map<String, Object[]> initialValue() {
            return (new HashMap<String, Object[]>());
        }
    };

    public static Pattern getCachedPattern(String namespace, String pattern) {
        return (getCachedPattern(namespace, pattern, 0));
    }

    public static Pattern getCachedPattern(String namespace, String pattern, int flags) {
        Map<String, Object[]> map = tls.get();

        Object[] entry = map.get(namespace);

        if (entry == null || !pattern.equals((String) entry[0])) {

            Pattern result = Pattern.compile(pattern, flags);

            map.put(namespace, new Object[] { pattern, result });

            return (result);

        } else {

            return ((Pattern) entry[1]);
        }
    }

    public static boolean mightBeEvil(String str) {
        // http://en.wikipedia.org/wiki/ReDoS

        if (!str.contains(")")) {

            return (false);
        }

        char[] chars = str.toCharArray();

        Stack<Integer> stack = new Stack<Integer>();

        for (int i = 0; i < chars.length; i++) {

            char c = chars[i];

            if (c == '(') {

                stack.push(i + 1);

            } else if (c == ')') {

                if (stack.isEmpty()) {

                    Debug.out("bracket un-matched in " + str + " - treating as evil");

                    return (true);

                } else {

                    int start = stack.pop();

                    if (i < chars.length - 1) {

                        char next = chars[i + 1];

                        if (next == '*' || next == '+' || next == '{') {

                            for (int j = start; j < i; j++) {

                                c = chars[j];

                                if ("+*{|".indexOf(c) != -1) {

                                    Debug.out("regular expression " + str + " might be evil due to '" + str.substring(start - 1, i + 2) + "'");

                                    return (true);
                                }
                            }
                        }
                    }
                }
            }
        }

        return (false);
    }
}
